The present invention relates to a technique for preventing a seek error of a head for a disk device including a recording medium, the seek error occurring when the head is brought into contact with a projected item existing between the head and the recording medium. The present invention also relates to a technique to prevent damage of the head due to the contact and a technique of seek control to prevent occurrence of another failure due to contact between the head and the recording medium.
A magneto-resistive (MR) head reproduces magnetic data recorded on a magnetic recording medium. In the data reproduction, by feeding a detection current to a magneto-resistive-effect element, a change in a leakage magnetic field of the medium is detected as a change of electric resistance (a voltage change). Use of an MR head is accompanied by a problem of contact between the MR head and a projected item existing between the head and the magnetic recording medium.
When the magneto-resistive-effect element of the MR head is brought into contact with the projected item, temperature of the element instantaneously increases. The temperature increase changes a resistance value of the element or the voltage change described above. This is called “thermal asperity (TA)”. When thermal asperity occurs during the reproduction of magnetic data recorded on a magnetic recording medium, the data cannot be correctly reproduced.
To cope with thermal asperity, a sector on which the thermal asperity has occurred is replaced with another sector or a track including the sector is replaced (JP-A-7-320216).
According to the invention described in JP-A-7-320216, the sector and the track associated with the thermal asperity are not used. Therefore, this invention is efficient to prevent errors during the data recording and reproducing operations. However, there further remain problems as follows. In seek control, a seek error occurs when the MR head passes over a track on which a projected item exists. When the head collides with the projected item, the head is damaged. The collision enlarges the projected item and hence thermal asperity occurs.